The torque required to initiate the operation of subsystems of heavy machinery such as the thresher unit of a combine harvester is greater than that required to operate it after it has been started. Indeed, it is possible to operate a combine harvester and maintain the thresher unit in operation using an engine that does not have sufficient torque to start the thresher unit from a standstill. This problem has become more prominent with the introduction of larger, high-capacity combine harvesters.
To provide an engine of sufficient power to be able to produce the full output torque needed to start the thresher unit would be wasteful both in terms of the initial cost of the engine and its running cost. It is clearly more efficient to design and dimension the engine only to be able to maintain all the subsystems of the harvester operating once it has been started.